Synopsis The pilot made a low pass over a neighbour's farm then pulled the aircraft into a climb. Suddenly the aircraft began rolling to the right, then descended vertically into the ground. Examination of the aircraft revealed that a structural failure of the right rear wooden wing spar had occurred. The pilot was fatally injured. The Board determined that the wing failure may have been the result of a previous occurrence involving damage to the right wing that was inadequately inspected both at the time of repair and during subsequent annual inspections. 1.0 Factual Information 1.1 History of the Flight After working on his farm since early morning, the pilot decided to conduct a local pleasure flight from a nearby farm strip where the aircraft was stored. The pilot refuelled the aircraft and then departed on his flight. As he had done in the past, the pilot made several low passes over a neighbour's farm. The neighbours went into the yard to wave to the pilot. As the pilot pulled the aircraft into a climb, the aircraft suddenly began rolling to the right, then descended vertically into a field of alfalfa. The neighbours called the police, and proceeded to the wreckage site where they found that the pilot had sustained fatal injuries. The accident occurred at about 2100 mountain daylight time1 (MDT)2, at latitude 5218'N, longitude 11402'W, in daylight conditions. 1.2 Injuries to Persons All times are MDT (Coordinated Universal Time [UTC] minus six hours) unless otherwise stated. See Glossary for all abbreviations and acronyms. 1.3 Damage to Aircraft 1.4 Other Damage 1.5 Personnel Information Pilot-in-Command Age - 47 Pilot Licence - PPL Medical Expiry Date - 01 Dec 1994 Total Flying Time - 1,000 hr Total on Type - 200 hr Total Last 90 Days - 4 hr Total on Type Last 90 Days - 4 hr Hours on Duty Prior to Occurrence - 9 hr Hours off Duty Prior to Work Period - 15 hr 1.5.1 Pilot Background The pilot had obtained his private pilot licence (PPL) in 1972 and had owned several light aircraft prior to the purchase of the accident aircraft in 1986. The family was unable to locate the pilot's log-book. 1.6 Aircraft Information Particulars Manufacturer - Taylorcraft Inc. Type - BC12D-85 Year of Manufacture - 1948 Serial Number - 12028 Certificate of Airworthiness (Flight Permit) - Valid Total Airframe Time - 1,668 hr Engine Type (number of) Continental C-85-8 - (1) Propeller/Rotor TypeMcCauley (number of) 1B90/CM7146 - (1) Maximum Allowable Take-off Weight - 1,280 lb Recommended Fuel Type(s) - 80\87 Avgas Fuel Type Used - Mogas 1.6.1 Maintenance History The aircraft had last been certified airworthy during a Certificate of Airworthiness (C of A) Renewal/100-Hour Inspection on 28 December 1993 at 1,652.4 airframe hours. The aircraft had been inactive for some time, and had been ferried to a maintenance facility for servicing. The aircraft technical logs indicate that in July 1985, at 1,571.2 airframe hours (96.8 hours prior to the accident), the aircraft had been damaged in an unreported occurrence while registered to a previous owner. The airframe log repair entry does not indicate the nature of the occurrence, but describes the replacement of a damaged right main landing gear leg, and repairs to the right wing tip bow and wing tip fabric. The engine log indicates that the crankshaft was inspected for run-out, and the propeller log entry indicates that blade straightening was carried out at an overhaul facility. The maintenance facility involved is no longer in business. A second technical log entry, in March 1989, at 1,624.3 airframe hours (43.7 hours prior to the accident), describes repairs including straightening the fuselage tail-post, the rudder and vertical stabilizer, and the horizontal stabilizer support. The crankshaft hub was magnaflux inspected and the propeller was repaired. A propeller entry in the Record of Installations and Modifications log indicates damaged by wind tip over - removed for repair and straightening. The aircraft repair facility indicated the owner had reported that the aircraft had been blown over on its back. 1.7 Meteorological Information There was no evidence found to indicate that the pilot had obtained a formal weather briefing prior to departure. Local weather conditions were reported as a partially cloudy sky and calm wind conditions. The nearest Environment Canada station at Red Deer, Alberta, reported scattered cloud at 9,000 feet, visibility 15 miles, temperature 16.2 degrees Celsius, dew point 7.3 degrees Celsius, and wind from 060T at 3 knots at 2100 MDT. Weather was not considered a factor in the occurrence. 1.8 Wreckage and Impact Information 1.8.1 Accident Site The aircraft struck the ground in a steep, nose-down attitude. The engine and propeller were pushed back and under the forward fuselage. One propeller blade was heavily twisted, and the leading edge was nicked in a manner typical of ground contact at a high power setting. The aft fuselage was buckled downwards just behind the wing trailing edge. Both wing leading edges were heavily impact damaged. Prior to the arrival of TSB investigators, the wreckage had been displaced, and the cabin area steel tubing had been cut apart with a jaws of life tool to remove the pilot. 1.8.2 Instrument Examination The following instruments were found with their pointers indicating the following readings: 3 For additional information see TSB Engineering Branch Report, LP 96/94 - Instrument Analysis. 4 For additional information see TSB Engineering Branch Report LP 95/94 - Wing Failure Analysis. The airspeed indicator and the vertical speed indicator dials were examined by the TSB Engineering Branch Laboratory to determine their pointer locations at impact, but no information was found3. 1.8.3 Spar Failure The right rear wooden wing spar was found with a vertical break inboard of the rear lift strut attachment fitting. The break exhibited an unusual, smooth, flat fracture surface over 75 per cent of the spar cross-section, with a splintered appearance on the remainder. The fracture surfaces appeared to have been rubbing against one another. The fracture coincided with the inboard edges of a pair of plywood spar doublers. Examination of these surfaces by the TSB Engineering Branch Laboratory4 and a wood products specialty facility determined that the fracture was a result of compression damage to the wooden wing spar prior to the accident. Compression damage is characterized by a buckling of the wood fibres, and will appear as streaks on the surface, substantially at right angles to the grain. Compression damage to wood can occur during the felling of trees, if they are roughly handled, or while a wooden component is in service on the aircraft. A typical example of in-service compression damage to wooden wing spars would be an occurrence where the lower surface of a wing tip contacts the ground heavily while the aircraft is in motion. There was no evidence found to indicate that the right rear spar had been replaced since original manufacture in 1948. A finite element computer simulation of the effect of this spar failure on the flight characteristics of the aircraft was prepared by the TSB Engineering Branch Laboratory facility. It indicated that the right wing would experience a loss of lift, and that the aircraft would enter an uncommanded roll to the right. 1.8.4 Engine and Fuel System Examination The engine was examined and found capable of normal operation. Fuel samples indicated that mogas was being used, although no evidence was found of the Supplementary Type Certificate (STC) approval which is required by Transport Canada (TC) regulation for use of this fuel. 1.8.5 Flight Controls Examination of the flight control systems did not indicate any discontinuities, and all controls were capable of normal operation. 1.9 Medical Information An autopsy and toxicological examination of the deceased pilot by the Provincial Medical Examiner indicated evidence of atherosclerotic coronary artery disease; however, it was not believed to have been the cause of or a contributing factor in the pilot's death. 1.10 Fire 1.11 Survival Aspects The aircraft was not fitted with a shoulder harness; however, the accident was considered non- survivable due to the magnitude of the deceleration forces. The lap-belts found installed in the aircraft were of the obsolete fabric-to-metal type. The aircraft was not equipped with an emergency locator transmitter (ELT); however, it was operating within a 25-mile radius of its home base, and, therefore, an ELT was not required. 1.12 Additional Information 1.12.1 Regulatory Requirements for Inspection of Wooden Spars TC has historically recognized the requirement for thorough, repetitive inspections of wooden components to ensure continuing structural soundness. An early TC Wooden Component Airworthiness Directive (AD), AD 63-3, was cancelled by AD CF-63-03R1, which indicated that, with the introduction of Chapter 571 of the Airworthiness Manual (AWM) and Airworthiness Manual Advisory (AMA) 571.101/5, all the necessary requirements were provided for the inspection of wooden components. A review of these documents indicates that Chapter 571, item G, page 18 in Appendix A of the Inspection Program for Small Aircraft requires inspection for poor condition of all components of the wing at 100-hour intervals. AMA 571.101/5, however, does not provide the Aircraft Maintenance Engineer (AME) with any inspection criteria for detection of compression failures in wooden spars. The AMA appears devoted to aircraft with wood skin rather than the more common combination of internal wooden structural members with metal ribs and fabric cover. There was no evidence found to indicate that the owner/pilot had selected and identified an inspection program in the aircraft journey log or provided the maintenance facility with a copy of an Inspection Check List as required by the AWM, Chapter 571. The inspection forms used by the maintenance facility during the last annual/100-hour inspection did not include a specific reference to visual inspection of the wing spar for condition as required by the AWM, Chapter 571. 1.12.2 Inadequate Inspection of Wooden Spars Although wooden spars are susceptible to deterioration due to age and damage to a far greater degree than other spar materials, the means of actually examining the wooden spars on the average light aircraft are very limited. The accident aircraft had only two inspection panels on the lower surface of each wing, and they were provided for control system access. Inspection of the wooden spar surfaces, especially to try to detect the evidence of compression damage, would be almost impossible without the installation of additional inspection panels.